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Tim H., HVAC Professional

Category: HVAC

Satisfied Customers: 3346

Experience: Experienced in all aspects of HVAC, both residential and commercial.

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I have a Sterling hanging natural gas furnace, 60,000 btu...has

Customer Question

I have a Sterling hanging natural gas furnace, 60,000 btu...has a honeywell sv9540 smart valve... takes 2min after burner comes on for the blower fan to be switched on, which causes overheating. I think the Honeywell sc9540 circuitry is failing. Do you agree?

Thanks for giving me the opportunity to help! That would be your fan control.

Tim H :

Is this a garage style heater?

Tim H :

Are you there?

Customer:

Yes. The LED on the SV9540 flashes 4 times, which is the code indicating open rollout switc, gas pressure too high, or airflow problem. My manual also says fan should kick on within 30sec...it takes over 2min so the controller kicks off the burner, then the fan finally comes on. Do the electronics in the sv9540 fail in this way (have you seen this before?)

Customer:

Can i just buy the electronics? I have looked on line and it seems they want to sell the whole package of valve and electronics which I do not think I need.

Customer:

It looks like they cost $250-300

Tim H :

The electronic fan timer normally turns the fan on, no the smart valve.

The honeywell manual says that it has an option for 30sec or 1min fan-on delay, and there is no other controller in the furnace

Customer:

is set by dip switches...

Tim H :

You should have either a fan timer or a circuit board

Customer:

have you dealt with the Honeywell sv9540?

Tim H :

I have

Customer:

have you seen the capability of it- has options for fan on delay, fan off delay and can be used for 2-stage systems. My furnace is single stage. i will have to check when I get home if the fan wiring connects to the contoller...

Customer:

I was looking for another circuit board but am unable to find one.

Tim H :

The Honeywell Smart valve is just like an ignition module. It has inputs from the limit, pilot ignitor, etc but like an ignition control, it doesn't directly control the blower. It relies on another board to do that.

Tim H :

I don't have the wiring diagram for your unit, but follow the leads from the blower and see where they go. Is this a garage heater or forced air furnace?

Customer:

garage heater

Tim H :

I would check the wiring diagram.

Tim H :

There should be a circuit board or fan timer that controls the blower. It may even just be a fan switch.

Customer:

so see if the leads go to the wiring harness that plugs into the beige part of the Honeywell sv9540 (the beige plastic part of the sv connects with 2 tamper-proof screws so I assume it can be changed out. So i need to vfy that the power leads for the fan (blower) go into this honeywell gizmo

Tim H :

If your blower is not coming on, this in turn is causing the limit to kick the burner off. I would find what controls your blower and start there.

Tim H :

There may not be a problem with the Honeywell Smart valve.

Customer:

OK

Tim H :

If I had the wiring diagram for this unit, it'd be helpful

Customer:

It is on the Sterling website- under model RF-60... does show a control board but is is not there. The brain seems to be the beige part of the Honeywell.

Yes, usually there is some other control or circuit board that controls the fan

Tim H :

You may not have the ST9160. These are just examples.

Tim H :

Do you have a readable wiring diagram?

Customer:

I was trying to get it off of Google again...Sterling RF60

Tim H :

OK, well when you get home, trace the wiring back from your fan or blower (not the inducer fan) and see where it goes, what controls it.

Tim H :

Once you find what is failing to bring the fan on, then you will solve the overheating.

Customer:

that makes sense. I see a "fan time delay switch" listed on the parts list, I assume it has to be ther somewhere, just not where it says on the diagram. So the Honeywell unit talks to that, then the delay switch kicks the power to the fan. I assume once I find it I can order a replacement using whatever part number it has on it. Thanks for straightening me out on that.

Tim H :

No problem. I really think you will find a bad fan switch. This is quite common on garage heaters.

Customer:

Somehow this is apparently causing the excessive delay.

Customer:

Good.

Customer:

Again, thank you.

Tim H :

Yes, it has a bimetal piece inside that heats up and makes a set of contacts to turn fan on. Probably bad.

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